Welding is used for many purposes, the most common being to join two pieces of metal together. In such a process, the abutting edges of the two pieces of metal are heated to an elevated temperature until they become molten, and a bead of molten metal is flowed from a welding rod or electrode along the molten edges to fuse the edges together. When the metal cools, it solidifies to form a unitary bond.
Many types of welding systems have been developed over the years. The most common are electric arc welding and gas welding. The present invention deals with gas metal arc welding (referred to as MIG). The MIG welding process is described in numerous articles, such as Gas Metal-Arc Welding (MIG Welding) by the ASM Committee on Gas Metal-Arc Welding and Flux-Cored Arc Welding of Steel, published in Metals Handbook, Vol. 6, Welding & Brazing, 8.sup.th Edition (1971). This article describes MIG welding as a process in which the heat for welding is generated by an arc between a consumable electrode and the work metal. The electrode is a bare solid wire that is continuously fed to the weld area and becomes a filler metal as it is consumed. The electrode, weld puddle, arc and adjacent areas of the base metal are protected from atmospheric contamination by a gaseous shield provided by a gas stream comprising a mixture of inert gases, typically a mixture of 90% argon and 10% carbon dioxide. During the process, the heat and the electric current causes the molten metal to splatter. Some of the splatter gets into the interior of the welding nozzle where it solidifies as slag on the interior wall. The slag, if allowed to continue to build up, reduces the size of the inner bore and smoothness of the nozzle, resulting in a reduction of gas flow and an alteration in the flow dynamics of the weld nozzle tip.
In the past, attempts have been made to prevent the build-up of slag in the nozzle tip by dipping the tip of the nozzle in a liquid such as a solution called Anti-Spat. Various means have also been tried to remove the slag, such as a rotating ream inserted into the nozzle tip to mechanically scrape the slag from the interior of the nozzle. Another technique has been to vibrate the nozzle tip in an effort to remove slag and other debris. In each case, the procedure requires a shutdown of the entire welding line so that the slag can be removed. Thus, the procedure has tended to be costly and time-consuming, particularly in automated production lines utilizing welding robotics.